Grain-size analysis from a drilling program 30 km west of Yellowknife defined three distinct sediment groups: a lowermost clay-rich unit (Group 1), a middle silt-rich unit (Group 2), and a sand-rich
upper unit (Group 3). Physical properties and mineralogy were investigated for two fine-grained clay samples by the GSC Sedimentology Laboratory and X-ray Mineralogy Laboratory, respectively; sediment texture was determined by the authors. Both
samples plot above the A-line of the Casagrande plasticity chart, indicating they are clays with intermediate to high plasticity, and classified by Atterberg limit analysis as inactive. The majority of nonclay minerals in the clay-size fraction are
quartz; and the remaining clay minerals are primarily detrital mica, chlorite, and kaolinite. Minor to trace amounts of mixed-layer clay minerals (most likely illite-smectite) are noted in the clay-size fractions, whereas only trace amounts are
observed in other group samples. These analyses confirm that the two samples fall within Group 1, and are glaciolacustrine, originating from glacial Lake McConnell (ca. 13.0-9.5 ka), and derived primarily from local granitic bedrock, with perhaps
some weathering or allogenic contribution, resulting in traces of mixed-layer clay minerals. Scanning electron microscope analysis revealed subrounded to subangular silt-size grains of detrital origin, randomly distributed in a clay matrix; with
possible evidence of minor compaction within the soil. Coarser grain size, higher quartz content, and only trace mixed-layer clay minerals suggest that Group 2 and 3 sediments originate from reworking and redeposition of Group 1 sediments within
lacustrine or alluvial settings. High ground-ice contents imply these sediments are prone to instability if thawed.

Summary

(Plain Language Summary, not published)Grain size analysis from a drilling program at a study site 30 km west of Yellowknife defined three distinct groupings of sediments: a lowermost
clay-rich unit (Group 1), a middle silt-rich unit (Group 2) and a sand-rich upper unit (Group 3). Physical properties, mineralogy and sediment texture were determined for two fine-grained clay samples from the lowermost unit. Analyses confirm that
the two samples fall within Group 1, and are glaciolacustrine, originating from Glacial Lake McConnell (ca. 13.0 ¿ 9.5 ka), and derived primarily from local granitic bedrock. High ground ice contents imply these sediments may be prone to
instability.